Digital Electronics

1
Digital Electronics

• Safety
• Introduction
• Basic Types of Multivibrators

2
Interest

• OnHand PDA Watch
• Casio Color Digital Camera Watch
• Sony Dog Robot
• Flat screen TVs
• Digital Cameras

3
Questions

• Q. What is the most interesting digital device
  you have used or seen?
• A. Various

4
A GOOD THING TO KEEP IN MIND!
SAFETY
5
THE BEST TOOLS EVER INVENTED HANDS!
6
SAFETY SHIELDS ARE EYE INSURANCE!
7
SAFETY SHOES ARE NOT FOR DEFEAT!
8
HEARING PROTECTION IS FOR WINNERS!
9
Always check Electrical Circuits Deenergized

• Discharge capacitors.
• Check Power Leads (T1-T3)
• Check Capacitors discharged.
• lt 30VAC is deenergized.

10
Electrostatic Discharge (ESD) is an Invisible
Threat.

• 1 touch can ruin this card.
• Wear a wrist strap.

11
General Safety Rules

• Do not work when you are tired or taking medicine
  that makes you drowsy.
• Do not work in poor light.
• Do not work in damp areas or with wet or damp
  clothing and shoes.
• Use approved tools, equipment, protective
  devices.
• Remove all metal items when working around
  exposed circuits.

12
General Safety Rules Continued

• Never assume that a circuit is off. Double-check
  it with an instrument that you are sure is
  operational.
• Buddy system is used at circuit breaker supplying
  power if working on circuit.
• Never override safety interlocks.
• Keep all tools and test equipment in good working
  condition.
• Discharge capacitors.

13
General Safety Rules Continued

• Do not remove grounds and do not use adapters
  that defeat the equipment ground.
• Use CO2 or halogenated-type fire extinguisher to
  put out electrical fires. Water conducts
  electricity! (i.e. galley fire in oven).
• Store solvents and other chemicals in appropriate
  areas. (i.e. fire personnel incident).
• Do not work on unfamiliar circuits.
• Do not cut corners or rush. No horseplay or
  practical jokes in the labs (i.e. throwing caps,
  meggering).

14
Shock Victim

• Do not become part of the problem.
• Use non-conductive belt and break free shock
  victim.
• Call for medical assistance. (911)

15
Review CPR

• Check for response.
• Have someone call 911.
• Clear airway.
• Look, listen and feel for breathing.
• Give 2 full breaths.
• 15 compressions (1 and 2 and 3)
• Continue till medical help arrives, you are
  relieved or are too tired to continue.

16
Questions

• Q1. Who is responsible for safety?
• A1. Everybody is responsible for their safety.
• Q2. What protects electronic circuits from ESD?
• A2. ESD packaging wrist straps.
• Q3. What is the worst electrical shock you have
  heard of or experienced?
• A3. Various.

17
Scientific Notation
18
Ohms Law
Given E Voltage I Current R Resistance
E
I
R
EIR
I E/R
R E/I
19
Multivibrators

• Monostable (One Shot) Multivibrator

-VCC
R1
R4
R2
R3
OUTPUT
C1
Q1
Q2
R5
0
C2
0
-
VBB
INPUT
-
20
Monostable Multivibrator

• .) Uses
• .) Used for pulse stretching
• .) Used in computer logic systems and
  Communication / Navigation systems.
• .) Operational Characteristics
• .) VBB is connected to the base of Q1 which
  places Q1 in cutoff.
• .) Q2 is saturated by -VCC applied to its base
  through R2.
• .) C1 is fully charged maintaining approximately
  -VCC on the base of Q2.
• .) A negative gate signal is applied to the base
  of transistor Q1 which turns Q1 on and drives it
  into saturation.
• .) The voltage at the collector of Q1 is then
  attached to the base of Q2 which turns Q2 off.
• .) C1 is discharged to attempt to keep VC at Q2
  constant. This maintains Q2 off.

21
Monostable Multivibrator

• .) When C1 is discharged, it can no longer keep
  Q2 off.
• .) Q2 turns on and saturates which causes its VC
  to go to approximately 0V.
• .) This 0V is applied to the base of Q1 which
  turns Q1 off.
• .) Q1s VC goes to -VCC and C1 charges to -VCC.
• .) The multivibrator will remain in this original
  state until another gate triggering pulse is
  received.
• .) Output from the circuit is taken from Q2s
  collector.
• .) Only one trigger pulse is required to generate
  a complete cycle of output.

22
Bistable Multivibrator

• .) Bistable (Flip - Flop) Multivibrator

-VCC
C3
OUTPUT 1
C4
OUTPUT 2
R5
R6
0
0
R3
R4
-
-
Q2
R2
R1
Q1
C1
C2
VBB
0
-
INPUT
23
Bistable Multivibrator

• .) Physical Description
• .) Multivibrator that functions in one of two
  stable states as synchronized by an input trigger
  pulse.
• .) Operational Characteristics
• .) Circuit is turned on.
• .) One of the two transistors will conduct harder
  and thereby reach saturation first. (Assume Q2)
• .) The 0V at the collector of Q2 is coupled to
  the base of Q1 which drives Q1 into cutoff.
• .) The -VCC at the collector of Q1 is coupled to
  the base of Q2 holding Q2 in saturation.
• .) An input trigger pulse is applied to the bases
  of both Q1 and Q2 simultaneously. Since Q2 is
  already in saturation, there is no effect on Q2.

24
Bistable Multivibrator

• .) The trigger pulse turns on Q1 and drives the
  transistor into saturation.
• .) The 0V on the collector of Q1 is coupled to
  the base of Q2 driving Q2 into cutoff.
• .) The -VCC on the collector of Q2 is coupled to
  the base of Q1 holding Q1 in saturation.
• .) This process will continue as long as there
  are trigger pulses applied to the circuit.
• .) The output frequency of the waveforms will be
  determined by the frequency of the input trigger
  pulses.

25
Astable Multivibrator

• .) Astable (Free - Running) Multivibrator

-VCC
OUTPUT 1
OUTPUT 2
R1
R4
R2
R3
0
0
C1
C2
-
-
Q2
Q1
26
Astable Multivibrator

• .) Physical Description
• .) Circuit has two outputs but no inputs.
• .) R1 R4, R2 R3, C1 C2, Q1 Q2 are as
  close as is possible in their operating
  characteristics.
• .) Operational Characteristics
• .) Circuit is turned on.
• .) Assume that Q2 conducts harder than Q1 and
  goes into saturation first.
• .) The 0V at the collector of Q2 is coupled to
  the base of Q1 which drives Q1 into cutoff.
• .) C2 begins to charge. C1 is at -VCC and this
  voltage is applied to the base of Q2 to hold Q2
  in saturation.

27
Astable Multivibrator

• .) After a finite period of time, (as set by the
  RC time constant of C2 and R3), C2 reaches a
  voltage value sufficient to snap Q1 on.
• .) Q1 quickly goes into saturation. The change in
  voltage from -VCC to 0Vcauses C1 to discharge.
• .) This voltage is coupled to the base of Q2
  Placing / holding Q2 in cutoff.
• .) C1 begins to charge and will snap Q2 on when a
  sufficient voltage value is reached.
• .) In Summary, whenever a transistor saturates,
  its VC will change from -VCC to 0V. This voltage
  will then be coupled to the base of the other
  transistor which will drive the other transistor
  into cutoff. The frequency of the output waveform
  will depend on the RC time constants established
  at C1R2 and C2R3.

28
Transistor Maintenance Chart
Transistor Testing

• This chart shows the readings for a good
  transistor.

29
Logic Probe Testing

• ( 5 V)

LOW indicator
Probe Tip
(Ground)
(Ground for TTL family)
HIGH indicator
D1
V
Red 5 V
HIGH indicator
LED 1
4
8
555 Timer IC
D2
2
R2
390?
Probe Tip
3
Input
D3
Outputs
6
R3
390?
R1
1
5
TTL Ground
TTL Ground
3.9 K?
LOW indicator
C1
LED 2
D4
0.01µF
Black Ground
Black Ground